Re: libstdc++/4367: Sparc atomicity.h routines can lock up on some OS.

[Phil Edwards <pedwards@disaster.jaj.com>]

The following reply was made to PR libstdc++/4367; it has been noted by GNATS.

From: Phil Edwards <pedwards@disaster.jaj.com>
To: eric.norum@usask.ca
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: libstdc++/4367: Sparc atomicity.h routines can lock up on some OS.
Date: Thu, 20 Sep 2001 11:23:25 -0400

 On Thu, Sep 20, 2001 at 02:50:01PM -0000, eric.norum@usask.ca wrote:
 > >Description:
 > The sparc version of the routines in atomicity.h can lock up
 > on operating systems which provide strict priority-based
 > scheduling (e.g. vxWorks, pSOS+, eCOS, RTEMS).  Here's the
 > scenario:
 > 1) Low priority task enters __exchange_and_add and sets
 >    the lock.
 > 2) While low-priority task is still active in
 >    __exchange_and_add a higher-priority task preempts.
 > 3) The higher-priority task enters __exchange_and_add and
 >    enters an infinite loop trying to set the lock.
 
 A classic case of priority inversion.  Wow.  I never imagined I'd be
 involved in one of those.  :-)
 
 One of the various Mars rover-type vehicles got locked up by priority
 inversion, I recall.
 
 -- 
 Would I had phrases that are not known, utterances that are strange, in
 new language that has not been used, free from repetition, not an utterance
 which has grown stale, which men of old have spoken.
                                      - anonymous Egyptian scribe, c.1700 BC